Commercially available instrumentation has made practical the routine determination of fluorescence lifetimes and dynamic depolarization parameters. Such determinations provide information not attainable from steady-state measurements. The acquisition of an SLM Instruments SLM-4800 LPS Subnanosecond Spectrofluorometer capable of such measurements would therefore significantly facilitate research on a number of biological systems currently being examined by investigators of the University of Virginia School of Medicine. Specific applications envisage the use of this instrument in detailed studies of membrane structure, the exchange of lipids and proteins between membranes, membrane fusion, lateral phase separation, protein conformation, protein aggregation, and macromolecular motion. The ability of dynamic depolarization measurements to reveal precise molecular rotational rates and degrees of constraint are of particular value in membrane fluidity measurements and in the elucidation of protein hydrodynamic parameters. Dynamic studies also facilitate the use of fluorescence energy transfer in molecular distance determinations since they provide unique information about orientation factors which have previously been the primary source of error in such experiments. Lifetime determinations enhance one's capability to examine heterogeneous systems and provide an accurate method for the detection of low levels of quenching. It is concluded that the acquisition of the SLM fluorometer is highly desirable and appropriate to the research efforts now being pursued in this institution.